Pipex, pipex and pipex or pipex, Pipex, pipex and pipex or pipex, Pipex, pipex and pipex or pipex, and did I mention Pipex ??
*****DONT***** Go with Tiscali !!!!!!!
1st rule is that you need to make sure that the day you get connected you have 10 days to make sure that your happy with their service. Check the download speeds and make a note about every call/complaint you make to your isp. Reason for the 10 days is that once the 10 days have expited your "cool off" period has expired and your locked into a 12 month contract.
Check the download speeds are roughly what you expect - Use Microsofts web site as download tester (fastest one I have found yet).
A good site for reference is as follows - check the "user comments on ISPs" section:
http://bbs.adslguide.org.uk/
Just check out the number of people that are trying to cancel their subscription or are complaining about performance.
My final tip is that you get what you pay for - Tiscali are 14.99 and complete tosh
and pipex at 23.00 are amazing
for EXACLY the same service (pipex thow in 1000 minutes of phone calls every month as well).